164 THE VOYAGE OF H.M.S. CHALLENGER. 



follow him, since, in spite of the extreme faultiuess of the original descriptions, the genus 

 is, according to Mr. Carter's own showing, recognisable. It is not known as a common 

 type in any seas but those of the West Indies, whence Carter describes several species. 



The systematic position of this genus is very doubtful. We include it here only on 

 the supposition that it has lost its microsclera. 



Agelas mauritianus, Carter sp. (PI. XXIX. fig. 10). 



1883. Edyon mauritianus, Carter, Ann. and Mag. Nat. Hist., ser. 5, vol. xii. p. 310, pi. xii. fig. 3, a, h. 



This species, so well characterised by its beautiful, mouiliform, echinating spicule 

 (PL XXIX. fig. 10), is represented in the collection by a single specimen of irregular massive 

 form and curiously cavernous structure, but of doubtful locality ; as the species has 

 already been described, and the characteristic spicule figured by Mr. Carter (and now 

 again by us), we need give no further details. 



A parchment label inside the bottle bears the words, " Station 135 1 60 fms." 

 Habitat. — Mauritius (Carter); off Tristan da Cunha (■?) (Challenger). 



Genus Echinodictyum, Ridley (PI. XXXII. ). 



1881. Echinodictyum, Eidley, Joiirn, Linn. Soc. Lond. (Zool.), vol. xv. p. 493. 



Skeleton reticulate. Megasclera smooth oxea in the fibre (sometimes accompanied by 

 partially projecting, smooth, slender styli) and spined styli echinating the fibre. No 

 microsclera. 



The genus Echinodictyum was estabhshed by Eidley {he. cit) for certain species of 

 various external habit, but agreeing in the possession of a reticulate skeleton consisting of 

 smooth oxeote megasclera united together in fibres by spongin, the fibre being echinated 

 by spined spicules projecting from it at right angles. Thus as regards spiculation it is 

 distinguished from Raspailia only by virtue of its oxeote instead of stylote main mega- 

 sclera ; the external form is, however, usually massive and the skeleton reticulate and 

 not radiate as is the case in Rasi^ailia. Subsequently some species were found in 

 which the fibre was accompanied by smooth slender styli sparingly associated with rather 

 than inserted in it ; the spicular distinction thus ceasing to be an entirely absolute one. 

 It is probable, however, that the Ectyonine arrangement, the relations of the fibre 

 and its spicules, and the bulky growth indicate that it forms a natural genus, distinct 

 from Raspailia with its slender cylindrical axes, radiate skeleton arrangement, and almost 

 exclusively stylote spicules. We include this genus amongst the Ectyoninse, like the 

 genus Agelas, on the supposition that it had at one time microsclera which it has now lost. 



